Furnace



Dec. 8, 1964 M. H. KUHNER 3,160,146

FURNACE Filed March 19, 1962 4 Sheets-Sheet 1 1 INVENTOR max H. Kuhne-r M. H. KUHNER Dec. 8, 1964 FURNACE 4 Sheets-Sheet 3 Filed March 19, 1962 INVENTOR 772 ax H. Kuh neT M. H. KUHNER Dec. 8, 1964 FURNACE 4 Sheets-Sheet 4 Filed March 19, 1962 LOW LOAD D A O L W O L INVENTOR. Flax H. Kuhner l'l/ H o ey 3,l ,lh Patented Dec. S, 1964 fifice 3,16%,146 FURNACE Max H. Kuhner, Ualrham, Mass, assignor to Riley Stoker Corporation, Worcester, Mass., a corporation of Massachusetts Filed Mar. 19, 1962, 8st. No. 180,503 Claims. (Cl. 122-473) This invention relates to a furnace and more particularly to apparatus arranged to provide for the flow of hot gaseous products of combustion over the heat exchange surfaces of a boiler for the production of steam.

In the operation f a steam generating unit the relationship between the burning of fuel and the generation of steam must be maintained very carefully. It is important that the fuel be entirely consumed and that the temperature of the resulting gases be reduced as greatly as possible to maintain the efficiency of the unit. At the same time, the passage of thermal energy from the hot gas to the water and steam in the heat exchange elements of the boiler must also be maintained very carefully in order that the resulting steam shall be at the proper temperature, this latter being necessary to enable the turbine with which the steam is used to operate efiiciently. At the same time, particularly in funnaces burning pulverized solid fuels, it is desired to have as little slag as possible pass into the convection surfaces of the boiler; it is desirable to obtain a continuous flow of molten slag from the bottom of the furnace. Obtaining all of these benefits in a single arrangement of furnace and fuel-burning apparatus is a very difficult matter. These and other difiiculties experienced with the prior art devices have been obviated in a novel manner by the present invention.

It is, therefore, an outstanding object of the invention to provide a furnace having a novel arrangement of furnace and fuel-burning apparatus which will permit com plete combustion of fuel with slagging limited to the lower part of the furnace and with the quality of steam maintained at a constant predetermined value.

Another object of this invention is the provision of a furnace burner arrangement in which the flow of air before mixing with the fuel does not flow in one portion of the burner only, but is selectively distributed around the burner opening.

A further object of the present invention is the provision of a burner having directional vanes and an air flow proportioning arrangement which permits the raising and lowering of the flame in the furnace, thus raising and lowering the elevation of the heat center of the flame for improved steam temperature and for the melting of ash on the furnace floor.

It is another object of the instant invention to provide a burner in which secondary air flow can be equalized or biased for top and bottom of the burner or, alternatively, can be entirely shut off when the burner is idle.

It is a further object of the invention to provide a furnace having a novel means for providing a hightemperature cell at the bottom of the furnace and for maintaining slag Within that cell so that it will not flow with the gas into other parts of the apparatus.

A still further object of this invention is the provision of a furnace having a high-temperature cell containing two sets of burners arranged in such a manner that the temperature of gases leaving the cell may be adjusted in order to regulate the superheat in a steam generating unit.

A still further object of this invention is the provision of a furnace having means for regulating the temperature of gases passing into convection passes having superheater elements, such regulation serving to maintain the temperature of superheated steam at a constant pre-determined value.

It is a still further object of the present invention to provide a furnace having means for regulating the process of combustion in a high-temperature cell in such a manner that the quality of slagging and the temperature of convection gases may be regulated and, nevertheless, a small capacity, low-cost unit may be constructed.

With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

FIG. 1 is a vertical sectional view through a fumace embodying the principles of the present invention, 4

FIG. 2 is an enlarged vertical elevational View of a portion of the invention taken on the line II-II of .FIG. 1,

FIG. 3 is a horizontal sectional view of the invention taken on the line IIIIII of FIG. 2,

FIG. 4 is a vertical sectional View of the invention taken on the line IVIV of FIG. 2, and

'FIGS. 5 through 10 are schematic views of the unit showing operation under various conditions.

Referring first to FIG. 1, wherein are best shown the general features of the invention, the furnace, indicated generally by the reference numeral 19, is shown inuse with a steam generating unit 11. The furnace is provided with a front wall 12, a rear wall 13, parallel opposed side walls 14, a bottom wall 15, and an inclined roof wall 16, all defining a vertically-elongated combustion chamber 17. Located on the front wall 12 adjacent the bottom 15 is an abutment 18 which extends toward the rear wall 13 a considerable distance and divides the combustion chamber 17 into a lower high-temperature cell 19 and an upper portion 21. The steam generating unit is provided with the usual steam-and-water drum 22 having steam separating and cleaning equipment in the usual manner. The steam-and-water drum is connected by downcomers (not shown) to longitudinal headers 23 underlying the side walls 14 and a transverse header 24 extending between the side wall headers, the header 24 being located nearer to the rear wall 13 than it is to the front wall 12. Water-wall tubes extend upwardly along the side walls 14 from the side wall headers 23 in the usual manner. From the transverse header 24 tubes extend in both directions along the bottom wall 15, some of the tubes passing up the front wall over the abutment 18 and others passing up the rear wall 13. A group of tubes leave the header 24- and form a screen 30 before joining the other tubes on the front wall 12 on the upper surface of the nose 18. The screen tubes lie for a considerable portion of their lengths in a somewhat inclined plane consitituting an extension of the upper surface of the abutment 18, but are bent into a series of vertical planes to define an opening 40 adjacent the floor 15. The rear wall 13 at its upper end adjacent the roof wall 16 is provided with an opening or gas off-take 25 leading to a back pass 26. The back pass is divided by a central bathe 27 into a front portion 28 and a rear portion 29, there being dampers 31 and 32 at the bottom of the portions 28 and 29, respectively, to control the flow of gas therethrough. The lower end of the back pass 26 is provided with a flyash-retaining hopper 70 which, in turn, is connected for gas flow through a primary air heater 8%). The air side of the ar heater 32 is provided with air from the forced draft fan 33 and its air outlet is connected to a duct 34.

In the lower part of the back pass 26 is located an economizer 35 for heating feed water. In the upper part of the rear portion 29 is located a low-temperature superheater 35, and in the front portion of convection-type reheater 36 whose outlet is connected to a reheated steam header 37. The outlet end of the low-temperature superheater 35 is connected by a pipe 38 to a high-temperature convective superheater 39 which discharges into a super- :3 6.; heated steam header 41. Extending forwardly from the rear wall 13 is a nose 42 which is just below the gas offtake 25 and which defines with the roof wall 16 a convection pass 50 in which the high-temperature superheater 39 is located.

The abutment 18 is provided with a downwardlydirected surface 43 which faces the bottom wall 15; between the nose 18 and the bottom wall 15 'is located a substantial vertical portion 44. Arranged behind the downwardly-directed surface 43 of the nose 18 is a series of burners 45, these being of the intertube directionalflame type shown and described in the patent to Craig No. 2,759,460. Arranged behind the vertical portion 44 is'a series of burners 46 of the same general type, but which will be described more fully hereinafter. The air flowing through the duct 34 is divided between a duct 47 having a damper 48 and leading to the burners45 on the-one hand, and a duct 49 having a damper 51 and leading to the burners 46 on the other hand.

The hopper 31 is connected to a vertical pipe 52 to an ejector device 53 provided with air by means of a fan 54. The ejector device 53 is connected by a pipe 55 to a flyash storage bunker 56 located at the upper part of the apparatus. The lower end of the bunker 56 is connected through a rotary valve 57 and a pipe 58 to one or more of the burners 45. Each of the burners 45 is provided with a set of vanes which are manually adjustable and which normally remain in a fixed angularity to the centerline of the burner.

The burners 46 are best explained in connection with FIGS. 2, 3, and 4 A series of water tubes 59, which originate in the transvrese header 24, overlie the vertical portion 44 of the front wall'under the abutment 18. These tubes are bent, as showninthe drawings, to provide narrow, vertically-elongated parallel openings 61, the central portion of which is provided with a fuel gun 62 and an igniter 63. Each group of openings 61 making up a burner 46 is surrounded by a housing 64 formed of sheet metal and provided with a suitable insulation material. Connected to the housing is the air duct 49 leading to the burner from the air heater 32. Extending vertically through the air duct 49 and then horizontally through thehon'zontal median of the burner 46 and the housing 64 is a dividing wall 65. This wall divides the burner into an upper portion 66 and a lower portion 67; it divides the air duct 49 into a forward portion 63 and a rear- Ward portion 69. In the. forward portion 68 of the air iuct is located a damper .71 connected for operation to a linear actuator such as a hydraulic cylinder 72. Simiiarly, the rearward portion 69 is provided with a damper 73 which is operated through suitable linkages by a :ylinder 74. The upper portion 66 of the burner is prosided with a set of horizontally-pivoted vanes 75 operated hrough suitable linkages by ,a cylinder 76. The lower )ortion 67 of the-burner is provided with a vertically- ;paced set of parallel vanes 77 swingable about horizontal gxes to adjusted positions under the. control of a cylinder {8. It may be observed in FIGS. 2 and 3 that the sides )f each individual burner are provided with somewhat rarrower slots 79 and 81 which are affected by the dividng wall 65 but which :are not influenced by the movement 1f the vanes 75 and 77. These slots are, however, provided vith fixed vanes 82 which are effective to direct air flow nwardly at the sides of each burner to prevent lateral lispersion of the air away from the fuel steam originating n -the guns 62. V

Returning now to FIG. 1, it can be seen that the superleated steam header 41 is provided with a temperaturendicating device '83 which is connected .by a line 84 to he input 'side of a main control 85 of the well-known type. iimilarly, the reheated steam header 37 is provided with temperature-indicating device 86 which sends a signal hrough a line 87 to the input of the main control 85, his signal being indicative of the temperature of reheated team passing to the turbine. A signal indicative of the load on the unit arrives at the inputof the main control through a line 166. The output side of the main control is connected by a line 88 to the actuating diaphragm of a spray desuperheater 89 which is operative to intro duce water into the pipe 38. The damper 48 in the duct 47 is positioned through suitable linkages by means of a cylinder 91 which is connected by lines 92 and 93 to the output of the main control 85. Similarly, the damper 51 in the duct 49 is positioned through linkages by a cylinder 94 which is connected for energization by lines 95 and 96 to the output side of the main control 85. The cylinder 76, which positions the vanes 75 in the upper portion 66 of the burner 46, is connected by lines 97 and 93 to the output side of the main control 85. In a similar manner, the cylinder 78, which positions the vanes 77 in the lower portion 67 of the burner 46, is connected by lines 99 and 1131 to the output side of the main control 85. The cylinder 72, which positions the damper 71, in the forward portion 68 of the duct 49, is connected to the output side of the main control 35 by lines 102 and 103, while the cylinder 74, which controls the position of the damper 73 in the rear portion 69 of the duct 49, is connected by lines 194 and 195 to the output side of the main control 85.

Extending upwardly from the air duct 47 is a supplementary duct 167 controlled by a damper 108. The air passing upwardly through the duct 167 passes into a box 105 from which it passes through tubes. 111 extending across the back pass 26 at an intermediate position between spaced sections of the economizer 35. The gases pass out of the tubes 111 into a box 112 and flow upwardly and into tubes 113 which extend again across the back pass 26 and terminate in a box 114 which exits into a duct 115 leading to an auxiliary portion of the apparatus which uses high temperature air. Such a use could be the pulverizer for the fuel which is to be burned in the burners, the high temperature air being useful in such a pulverizer to promote the drying of the fuel.

The operation of the apparatus will now be readily understood in view of the above description. To begin with, it will be understood that the main control 85 receives signals of superheated steam temperature, reheated steam temperature, and load through the lines 84, 87, and 166, respectively. These constitute the input signals for the main control. The output signals which pass through the lines 88, 97, 93, 99, 161, 104, 105, 162, 163, 92, 93, 95, and 96 serve to position the upper vanes 66 of the burners 46, the lower vanes 77 of the burners 46, the dividing dampers 71 and 73 associated with the burners, and the dividing dampers 48 and 51 associated with the ducts 47 and 49, respectively, as well as the operation of the des'uperheater 89. The main control may be set up so that these various elements occupy pro-determined positions at various loads on the device. As has been stated, a signal indicative of load is introduced into the main control 85 through a line 106 which is connected to an air-flow measuring device connected in an air flow duct of the system and which, therefore, produces a signal indicative of air how and, therefore, of load on the unit, The furnace 10 operates in the usual way to provide hot products of combustion for the steam generating unit 11. Water passes downwardly from'the steam-andwater drum 22 into the lower headers 23 and 24 from which it is distributed upwardly through the walls of the furnace in tubes 59, as well as in the screen 30. The

. steam which is released in the steam-and-water drum 22 after passage through the water walls of the furnace is then passed into the low-temperature 'superheater 35 in wh1ch it flows upwardly in counterfiow to the flow of gas from the furnace, which. gas passes downwardly through the rear portion 39 of the back pass 26. The steam then flows through the pipe 38 where it is subjected to a degree of desupe'rheating dependent on the signal in the line 88 leading to the desuperheater $1 It then passes into the high-temperature superheater 39 which lies in the convection pass 50, located between the nose 42 and the roof wall 16. The steam flows into the superheated steam header 41 and passes to the high-pressure section of the turbine. In. returning from the turbine, the steam is introduced and passed through the reheater 56. It flows from there upwardly in counterflow to gas passing downwardly through the front portion 28 of the back pass and exits into the reheated steam header 3? from which it passes into the low-temperature section of the turbine.

Each burner 45 on the downwardly-directed surface of the abutment 18 provides a flame which, although its position and nature may be adjusted, is usually fixed; it is contemplated that the direction of flow of the fuel and air from this burner for combustion takes place generally parallel to the inclined plane of the screen 39 and of the upper surface of the abutment 18. The burners 46, which are mounted on the vertical portion 44 of the front wall underlying the abutment 18, are adjusted with load either as to the spread of the flame or the direction of the flame, or both. In addition, by manipulation of the dampers 48 and 51, the distribution of air between the burners 45 on the one hand and the burners 46 on the other hand may be adjusted. This may be done to control superheat and also to control furnace conditions. The flames from the burners 45 and the burners 46 mix in the high-temperature cell 19 and combustion is substantially completed in that cell. This means that the molten slag from the incombustible materials in the fuel will be formed in this chamber, will strike the walls, and will flow downwardly through the slag tap opening in the bottom wall 15. The tendency of the flame from the burners 45 and 46 in the downward direction to pass close to the bottom wall 15 is evident from the illustrations. Any slag which is carried in the gas as it leaves the high-temperature cell 19 will either strike the portions of the screen 3t) which are in close-tube relationship or will be cooled by passage through the portion of these tubes which are spread to provide a gas outlet 49.

It will be seen from an examination of the details of the burner 46 in FIGS. 2, 3, and 4, that this construction obviates certain dilflculties experienced in the past with intertube burners of this kind. Considerable difficulty has been experiencved with the air arriving through a duct corresponding to the duct 49 and flowing in one part of the burner only, usually through the upper part. This means that the fuel from the gun 62 is projected directly into the furnace along with the primary air,- while the secondary air arriving in the duct has a tendency to rise immediately from the burner and not contact the fuel at all, thus promoting late ignition high in the furnace. With the present invention, the air is suitably divided between the upper and the lower portion of the burner so that there is no such bypassing. The air may be so divided that the mixing between the secondary air and the fuel arriving in the fuel gun 62 may be controlled. Manipulation of the vanes 75 and 77, it will be understood, will permit the secondary air and, therefore, the flame, to be directed upwardly or downwardly; also, the flame may be controlled in shape from a narrow flame to a wide fan-type flame. The manner in which these elements may be manipulated to control superheat through the medium of the main control 85 is shown in the schematic drawings in FIGS. 5 through 10. FIGS. 5 and 6 show the way in which the spreading of the flame from the burners 46 may be used to maintain superheat at a predetermined value. As shown in FIG. 5, at low load, where there is a tendency for superheat to be low, the flames from the burners 46 are produced as narrow flames. They do not mix as soon with the flames from the burners 45 so that the gases which flow up into the furnace are higher in temperature. This means that the temperature of gases arriving in the convection pass 50 and passing over the convection superheater 39 will be at a higher temperature so'that there will be a tendency to maintain superheat at a high value despite the fact that the furnace is operating at low load. On the other hand, at high load, as shown in FIG. 6, where one desires to keep the superheat temperature down, the flame from the burner 46 is provided as a wide, fan-type flame which mixes quickly and readily with the fuel and air components or flame from the burners 45. This results in a condition in which the gases which reach the convection pass and pass over the superheater are at a lower temperature than would otherwise be the case.

FIGS. 7 and 8 show the unit being operated for control of superheat by making use of the ability to control the direction of the flame from the burner 46 by manipulatting the vanes 75 and 77 and also by manipulating the flow of air under the control of the dampers 71 and 73. At low load, as shown in FIG. 7, the flame from the burners 46 is directed downwardly toward the bottom wall 15 of the furnace; the mixture with the flame from the burners 45 is delayed so that an elongated flame is produced which extends well up into the combustion chamber 17; this means that the temperature of gases passing into the convection section is high, which is a desirable characteristic. On the other hand, at high load, as shown in FIG. 8, the flame is directed upwardly and immediately contacts the flame from the burner 45 producing intense turbulence in the high temperature cell 19 and more or less complete combustion before the gases leave the high-ternperature cell through the openings 46 in the screen 30. This manner of operation results in gas at lower temperature than would otherwise be the case passing over the convection superheater elements, again tending to keep the temperature of superheated steam from exceeding the desired value at high load.

FIGS. 9 and 10 show the manner in which the biasing or dividing of the air between the ducts 47 and 49 passing to the burners 45 and 46, respectively, may be used to maintain superheat temperature constant. In FIG. 9, which is the low load condition, a large amount of air is passed into the burners 46 by opening the damper 51, while a lower amount is introduced into the burners 45 by throttling the damper 48, thus producing a flame from the burners 46 which dominates the situation and produces an elongated flame of high temperature gases passing well up into the furnace, so that the temperature of gasses passing over the convection superheater are at a high value and superheat is maintained high despite the fact that the operation is at low load. On the other hand, at high load, as shown in FIG. 10, the damper 48 is opened while the damper 51 is moved toward closed position and the air mixture in the burners 45 dominates the situation. With regard to the manner in which sufficient fuel is supplied when the dampers 48 and 51 are manipulated it should be pointed out that a control means is introduced as standard practice in all boilers. This control means serves to maintain the fuel-airratio at a preset value. The details of this control means are not shown in the present application since it is considered to be conventional practice to provide such fuel-regulating means. Since the burners are directed downwardly in the cell, there is a considerable tendency to complete the combustion in the high-temperature cell 19 and produce a very short flame which hardly leaves the high-temperature cell through the opening 40. The net effect is low temperature gas passing into the convection passes and afliecting the temperature of superheat. It will be understood, of course, that, despite broad temperature'changes produced by the manipulation of the burners, it will still be necessary to provide a fine adjustment of superheat temperature by means of the desuperheater 89.

The passage of flyash and cinders from the hopper 31 downwardly through the pipe 52 and its projection by means of the fan 54 and the ejector device 53 through the pipe 55 to the bunker 56 is evident. The flyash flows from the bunker through the rotary valve 57 which controls the flow according to the speed of the motor driving the rotary valve so that the-rate of flow of fiyash is under control at all times. This fiyash passes through the pipe 58 into the burners 45' where it mixes with the fuel-and air mixture which moves with them into the high-temperature cell 19. The high temperatures existing in the turbulent gas mass will tend to melt down the flyash and cinders and cause the resulting slag to flow outwardly through the slag opening 66 in the bottom wall of the furnace. The slag or molten fiyash and cinders is, of course, much easier to dispose of than the bulky, dirty dry fiyash.

The opening and closing of the damper Hi8 causes a heating of a portion of the incoming air for use in the pulverizer. The passage of the air in heat exchange relationship with the gases in the back pass by passing it through the tubes 111 and 113 is evident and this operation promotes the overall eiiiciency of the steam generating unit by reducing the outlet gas temperature.

It is obvious that minor changes may be made in the form and construction of the invention without departing from the material spirit thereof. It is not, however, desired to confine the invention to the exact form herein shown and described, but it is desired to include all such as properly come within the scope claimed.

The invention having been thus described, what is claimed as new and desired to secure by Letters Patent,

l. A furnace, comprising (a) a plurality of generally parallel water tubes forming a vertical wall, some of the tubes being bent out of the plane of the wall to define a group of adjacent, narrow, vertically-elongated openings through the wall,

(b) a housing external or" the walls and enveloping the said group of openings,

(c) a fuel pipe extending through one of the openings centrally of the said group, I

(d) an air duct connected to the housing, r t

(e) a horizontal wall dividing the duct and housing into two equal upper and lower' portions located above and below the fuel pipe, respectively,

(1) a first group of vanes located adjacent the tubes in the upper portion of the housing,

(g) a second group of vanes located adjacent the tubes in the lower portion of the housing,

(h) an independently-operated air-regulating damper in each portion of the air duct,

(i) and control means'for regulating independently the settings of the dampers to regulate a quality of the flame, the'control means operating at low load to direct the first and second groups of vanes toward one another and to open the damper in the upper portion of the duct to produce a narrow flame, the control me'ans operating at high load to direct the first and second groups of vanes away from one another and to close the damper in the upper part of the duct to produce a wide flame.

2. A furnace, comprising (a) a front wall, a rear wall, a bottom wall, a roof wall, and two opposed side walls defining a verticallyelongated combustion chamber,

(b) an abutment formed on the front wall having a downwardly-directed surface defining with the bottom wall a high-temperature cell, there being. a substantial portion of the front wall extending from the abutment to the bottom wall,

(0) a nose formed on the rear wall immediately under the gas off-take, Y 7 (d) a plurality of directional-flame burners mounted on the downwardly-directed surface of the abutment,

(e) a plurality of burners mounted on the said vertical portion of the front wall,

(f) a back pass connected to the upper end of the combustion chamber by a gas off-take,

(g) a header underlying each side wall from which water tubes extend upwardly over the side wall surfaces,

(h) a transverse header extending etween the two side wall headers from which water tubes extend over the bottom wall and up the front and rear walls,

(1) a plurality of water tubes forming a screen extending in a plane from the transverse header to the rearwardmost portion of the abutment, the tubes being bent out of the said plane in their rearward portions to provide large openings through the screen,

(j) a plurality of generally parallel water tubes forming the said vertical portion of the front wall between the abutment and the bottom wall, some of the tubes being bent out of the plane of the wall to define a group of adjacent narrow vertically-elongated openings through the wall, a housing external of the walls and enveloping the said group of openings, a fuel pipe extending through one of the openings centrally of the said group, an air duct connected to the housing, a horizontal wall dividing the duct and housing into two equal upper and lower portions, 21 first group of vanes located adjacent the tubes in the upper portion of the housing, a second group of vanes located adjacent the tubes in the lower portion of the housing, an air-regulating damper in each portion of the air duct, and means for regulating the settings of the dampers to regulate a quality of the flame, the control means operating at low load to direct the first and second groups of vanes toward one another and to open the damper in the upper portion of the duct to produce a narrow flame, the control means operating at high load to direct the first and second groups of vanes away from one another and to close the damper in the upper part of the duct to produce a wide flame,

(k) fiy-ash collecting means located in the back pass,

' a storage bunker located above the burners, means for carrying ily-ash from the collecting means to the storage bunker, and a conduit leading from the bunker to the burners for permitting fly-ash to flow by gravity to the burners,

(I) a primary air heater to which the back pass is connected to heat air for direct use in the burners, a secondary air heater located in the back pass and receiving a portion of the heated air from the air heater and heating it further for use in auxiliary equipment associated with the furnace,

(m) a convection superheater located in the said pass, and means for regulating the burners to maintain the temperature of superheated steam at a predetermined value.

3. A furnace, comprising (a) a front wall, a rear wall, a bottom wall, a roof wall, and two opposed side walls defining a verticallyelongated combustion chamber,

(1)) an abutment formed on the front wall having a downwardly-directed surface defining with the bottom wall a high-temperature cell, there being a substantial portion of the front wall extending from the abutment to the bottom wall,

(c) a first set of directional-flame burners mounted on the downwardly-directed surface of the abutment,

(d) and a second set of burners mounted on the said vertical portion of the front wall to produce a fixed flame,

(2) a convection pass receiving products of combu tion from the upper part of the combustion chamber, (f) a convection superheater located in the said pass, (g) control means to regulate the burnersto maintain the temperature of superheated steam at a predetermined value, the said control means operating on one of the sets'ofburners to affect the amount of impingement of the flame from the first set of burners on the flame from the'seco'nd set of burners to cause them to operate with a spread flame at one end of the load range and with a narrow flame at the other end of the load range.

4, A furnace, comprising (a) a front wall, a rear wall, a bottom wall, a roof wall, and two opposed side walls defining a verticallyelongated combustion chamber,

(b) an abutment formed on the front wall having a downwardly-directed surface defining with the bottom wall a high-temperature cell, there being a substantial portion of the front wall extending from the abutment to the bottom wall,

(c) a first set of directional-flame burners mounted on the downwardly-directed surface of the abutment,

(d) and a second set of burners mounted on the said vertical portion of the front wall,

(e) a convection pass receiving products of combustion from the upper part of the combustion chamber,

(f) a convection superheater located in the said pass,

(g) control means to regulate the burners to maintain the temperature of superheated steam at a predetermined value, the said control means operating on one of the sets of burners to change the angular relationship with the other set to affect the amount of impingement of the flame from the said one of the sets of burners on the flame from the other set, so that the angle between the lines of action of the sets is large at one end of the load range and is smaller at the other end of the load range.

5. A furnace, comprising (a) a front wall, a rear wall, a bottom wall, a roof wall, and two opposed side walls defining a verticallyelongated combustion chamber,

(b) an abutment formed on the front wall having a downwardly-directed surface defining with the bot- 10 tom wall a high'temperature cell, there being a substantial portion of the front wall extending from the abutment to the bottom wall, (0) a first set of directional-flame burners mounted on the downwardly-directed surface of the abutment, (d) and a second set of burners mounted on the said vertical portion of the front wall,

(e) a convection pass receiving products of combustion from the upper part of the combustion chamber, (7) a convection superheater located in the said pass, (g) control means to regulate the burners to maintain the temperature of superheated steam at a predetermined value, the said control means operating on the sets of burners in such a way that the fiow of air through one of the sets is larger than the flow of air through the other set at one end of the load range and in such a way that the flow of air through the said other set is larger than the flow of air through the said one of the sets at the other end of the load range to affect the amount of impingement of the flame from the said one of the sets of burners on the flame from the other set.

References Cited in the file of this patent UNITED STATES PATENTS 2,222,769 Hardgrove Nov. 26, 1940 2,582,830 Hawley Jan. 15, 1952 2,811,953 Feeley Nov. 5, 1957 2,947,289 Miller Aug. 2, 1960 3,063,431 Miller Nov. 13, 1962 3,095,864 Miller July 2, 1963 FOREIGN PATENTS 720,666 Great Britain Dec. 22, 1954 

3. A FURNACE, COMPRISING (A) A FRONT WALL, A REAR WALL, A BOTTOM WALL, A ROOF WALL, AND TWO OPPOSED SIDE WALLS DEFINING A VERTICALLYELONGATED COMBUSTION CHAMBER, (B) AN ABUTMENT FORMED ON THE FRONT WALL HAVING A DOWNWARDLY-DIRECTED SURFACE DEFINING WITH THE BOTTOM WALL A HIGH-TEMPERATURE CELL, THERE BEING A SUBSTANTIAL PORTION OF THE FRONT WALL EXTENDING FROM THE ABUTMENT TO THE BOTTOM WALL, (C) A FIRST SET OF DIRECTIONAL-FLAME BURNERS MOUNTED ON THE DOWNWARDLY-DIRECTED SURFACE OF THE ABUTMENT (D) AND A SECOND SET OF BURNERS MOUNTED ON THE SAID VERTICAL PORTION OF THE FRONT WALL TO PRODUCE A FIXED FLAME, (E) A CONVECTION PASS RECEIVING PRODUCTS OF COMBUSTION FROM THE UPPER PART OF THE COMBUSTION CHAMBER, (F) A CONVECTION SUPERHEATER LOCATED IN THE SAID PASS, (G) CONTROL MEANS TO REGULATE THE BURNERS TO MAINTAIN THE TEMPERATURE OF SUPERHEATED STEAM AT A PREDETERMINED VALUE, THE SAID CONTROL MEANS OPERATING ON ONE OF THE SET OF BURNERS TO AFFECT THE AMOUNT OF IMPINGEMENT OF THE FLAME FROM THE FIRST SET OF BURNERS ON THE FLAME FROM THE SECOND SET OF BURNERS TO CAUSE THEM TO OPERATE WITH A SPREAD FLAME AT ONE END OF THE LOAD RANGE AND WITH A NARROW FLAME AT THE OTHER END OF THE LOAD RANGE. 